PROJECT SUMMARY. Diabetes has been identified as an epidemic in the United States and its deleterious effects have broad implications for the musculoskeletal system. Individuals with diabetes are at increased risk of tendon injury as well as tendon-limited joint mobility, which has been suggested to be an inciting factor in the development of plantar ulcers and lower limb loss. Despite the potentially severe sequelae of diabetes-related tendon complications, there is a lack of non-invasive tools to assess tendon in vivo particularly at smaller levels of tendon architecture. Magnetic resonance-based diffusion tensor imaging (DTI) has the potential of being applied to tendon to non-invasively assess tendon microstructure. DTI uses the direction and freedom of water molecule mobility in fiber tracts to characterize tissue microstructure. Tendon has traditionally been very difficult to image with DTI, however, a newly-improved DTI pulse sequence has allowed for the application of this technique to tendon tissue. The long-term goal of this fellowship application is to optimize tendon healing from injury and metabolic disease by bridging basic science and clinical research approaches. As a step toward that goal, this proposal compares DTI to direct testing of human tendon tissue and applies DTI to a clinical population of individuals with and without diabetes to improve our understanding of diabetes-related changes to tendon health. This objective will be accomplished using a combination of ex vivo and in vivo approaches. Aim 1 uses Achilles tendon specimens collected from individuals undergoing lower extremity amputation. DTI indices are compared to direct measurement of tendon microstructural properties to improve our ability to interpret DTI indices. The tendon is imaged ex vivo with DTI and then analyzed using quantitative polarized light imaging to measure collagen alignment, biochemical analysis to quantify accumulation of advanced glycation endproducts, and tensile mechanical testing. Aim 2 leverages DTI to quantify in vivo microstructural properties of the Achilles tendon to identify diabetes-related changes to tendon health. DTI indices will be compared in a group of individuals with compared to individuals without diabetes. The outcome of the proposed study will bridge basic science approaches of tendon assessment with emerging non-invasive imaging methods of assessing tendon microstructure as well as improve our understanding of diabetes-related alterations in tendon microstructure. This innovative approach will help identify parameters that could serve as imaging biomarkers of tendon injury and disease for future clinical, interventional studies.